This invention relates to radiation scanning systems and of particular importance to radiation scanning systems that require two scanning speeds, a high scanning speed in one direction and a low scanning speed in a second direction. The radiation scanning system of the invention belongs to the class of radiation scanning systems in which a scene is generated by two mechanisms, one operating at the high scanning speed in order to give a scan line and the other operating at a lower scanning speed to give a frame.
U.S. Pat. No. 4,210,810 disclosed a radiation scanning system that includes a detector, a transfer lens forming a real image of the detector, a rotary scanning means interposed between the transfer lens and the detector image in such a way that as the rotary scanning means is rotated, the detector image moves in a circular locus. A concave substantially spherical mirror is concentrically disposed with respect to the detector locus, said locus being at the focal surface of the mirror so that for different rotational position of the rotary scanning means differently directs parallel bundles of rays emanate from the mirror all intersecting at a pupil. A second scanning means is also located at said pupil. The two scanning means provide orthogonal line in frame scans.
U.K. Patent Application GB 2 129 958 also discloses a transfer lens system for a radiation detecting system.
The efficiency of the scan apparatus is determined by the scan rotational angle of a polygon scanner while focused energy is maintained on only one facet of the polygon. The scan efficiency can be improved by positioning the image of the detector close to the scanning surface of the scanner. When this is done light leaving the polygon leaves at a large angle due to the required large rotation angle of the polygon. The larger angle that the energy leaves the reflective facets of the polygon results in a larger collimating mirror such as a spherical mirror and results in increased difficulty in obtaining good imagery.